1. Field of the Invention
The invention relates to computing systems and, more particularly, to file system catalogs.
2. Description of the Related Art
As is well known, file system backups in computing systems may take a considerable amount of time and storage space. In many file systems, a significant portion of the data is not changed after its creation or after an initial period of access. Generally speaking, the conventional approach to data backup includes periodically performing a full backup of everything in the file system, for example once a week or once a month, and performing incremental backups between full backups, for example every day. Typically, this conventional approach makes a copy of all of the data in the file system, even though a large percentage of that data may not have changed since the previous full backup. Consequently, using the conventional approach, data may be backed up on a full backup even though one or more copies of that data may already exist on previous full backups. In order to perform a restore from a previous backup, a most current full backup is typically restored, and then any changed data since the full backup is restored from incremental backups performed subsequent to the current full backup.
One alternative for improving the performance of backups is to utilize an approach sometimes referred to as “synthetic full backups”. In a synthetic backup, instead of performing a full backup by backing up all of the data on a file system, a copy of a previous full backup is used to determine which portions of the file system will be included in the backup. For example, data that has been deleted from the file system since the last full backup are subtracted from the full backup and data that is new or has changed on the file system are added to the full backup. In this manner, a new “synthetic” full backup is generated.
As noted above, incremental backups may be utilized to backup changes to data since the last full backup. Such an approach may have the advantage of only backing up files that are new or files that have changed since the last backup. However, in order to provide a true image restore (i.e., to restore only files that existed at the time of the incremental backup) or to create a synthetic full restore (i.e., an image that is equivalent to a full taken at the time of the incremental), the exact “state” of the file system at the time of the incremental must be preserved. Catalogs which are used for incremental backups that are used for true Image restore or synthetic full images may generally require the same amount of disk space as a normal full backup. Consequently, backups for large file systems which utilize incremental backups may entail very large catalogs. For example, catalogs for some large file systems may exceed 500 GB. Because of the significant storage space required for these catalogs, an enterprise may be reluctant to use features (e.g., true image restore or synthetics backups) which would generate large catalogs.
Accordingly, an efficient method and mechanism for managing data backups and restores is desired.